The present invention relates to a device for purifying exhaust gases of the type utilizing catalysts for converting the toxic components thereof such as carbon monoxide (CO) and hydrocarbons (HC) into nontoxic or harmless gases in a very efficient manner.
The exhaust gases emitted from internal combustion engines contain toxic gases or pollutants such as carbon monoxide (CO), hydrocarbons (HC) an nitrogen oxides (NOx), and in order to remove such pollutants various devices have been devised and demonstrated. Among them, the devices utilizing catalysts (to be referred to as the catalytic converters in this specification) are most advantageous because they are simple in construction and may be incorporated in the exhaust systems of internal combustion engines without requiring modifications of the engines and may not adversely affect the performance of the engines.
The conventional catalytic converters use various types of catalysts such as pellet or bead type, honeycomb type and so on. The bead or pellet type catalyst has greater attrition loss so that if the beads or pellets should be discharged into the atmosphere, they will cause a secondary air pollution problem. When the temperature of a honeycomb type catalyst rises excessively the catalyst will be melted away. Furthermore the honeycomb type catalyst has a defect that it is easily susceptible to damage due to vibrations or shocks.
The catalytic oxidation of carbon monoxide and hydrocarbons for converting them into water and carbon dioxide is an exothermic reaction. When a catalytic converter is used in conjunction with an internal combustion engine with a total stroke volume from 1,000 to 2,000 cc, the temperature of the catalytic layer reaches as high as 500.degree. to 600.degree. C. In case of automotive engines, a relatively large quantity of carbon monoxide and hydrocarbons is discharged when the engine is running under a greater load, when the engine braking is applied or when misfiring occurs. In case of two cycle engines, a large quantity of unburned hydrocarbons is discharged because of the operating principles of, and fuel used in such engines, so that the temperature of the catalyst rises as high as 1,000.degree. C. As a result, the performance of the catalyst is adversely affected.